The Genetics and Pathology of Rhizoctonia Solani

The objective of this paper is to review the genetical and pathological research on Rhizoctonia solani Kuhn from 1965 to the present. In 1965, a symposium, Rhizoctonia solani: Biology and Pathology, was held at Miami, Florida. At this meeting the characteristics of the imperfect stage were defined (60) and the perfect stage accepted as Thanatephorus cucumeris (Frank) Donk (79). It was recognized, however, that T. cucumeris was a collective species and that its nomenclature was not expected to remain stable (79). The past 15 years have been a productive period of research on the pathogen and on the diseases it causes. A number of disease resistant cultivars have been reported and disease control measures have been recom­ mended. The principle most helpful to plant pathologists during this period has been the anastomosis group (AG) concept. This scheme was first suggested in Germany by Schultz in 1937 (74) and later developed by Richter & Schneider in 1953 (66); in Japan by Watanabe & Matsuda in 1966 (82); and in the United States by Parmeter et al in 1969 (59). According to this scheme fusion occurs only between isolates of the same AG. Parmeter et al proposed four AGs (59); Kuninaga et al (49) have expanded the concept to include six AGs and Ogoshi (55) has proposed two subgroups within both AG 1 and AG 2. I will discuss each anastomosis group separately in this paper.